A known pressure generator is disclosed in Japanese Patent Laid-Open Publication No. 1(1989)-223063. This pressure generator is installed in a brake apparatus provided with wheel brakes to apply fluid pressure to the wheel brakes which in turn apply a brake force to the wheels.
This known pressure generator includes a master cylinder, a hydraulic pump and a pressure supply device. The master cylinder is provided with a cylindrical body in which is defined a cylinder bore, and a piston which is slidably disposed in the cylinder bore to form a pressure chamber between the front side of the piston and the cylinder body, and with the pressure chamber being connected to the wheel brake. When the brake pedal is operated, the piston is advanced to generate brake pressure which is applied to the wheel brake.
The hydraulic pump draws in and discharges fluid pressure, thus supplying the fluid pressure to the wheel brakes when one or more of the wheels tends to be slipping (spinning) in relation to the road surface. The pressure supply device supplies brake pressure, corresponding to the operation of the hydraulic pump, to the hydraulic pump independently of the master cylinder.
Under a normal brake operation when the brake pedal is operated, brake pressure is generated in the pressure chamber of the master cylinder by the advance of the piston. The brake pressure is applied to the wheel brake to apply a braking force to the wheel. When a condition occurs where the vehicle wheels are slipping (spinning) during acceleration, the hydraulic pump supplies brake pressure to the wheel brakes to prevent the wheels from slipping. At this time, the pressure supply device generates the brake pressure, after supplying brake pressure to the hydraulic pump independently of the master cylinder, so that brake pressure is supplied to the wheel brake smoothly.
However, by virtue of the presence of the pressure supply device, the pressure generator having the construction as described above is undesirably large in size and complex in construction.
In light of the foregoing, a need exists for a pressure generator which is relatively simple in structure and small in size, while at the same time providing an efficient pre-pressurizing mechanism in a brake fluid pressure control apparatus.